Massey Ferguson 4346.03 – ECU (Engine Control Unit): DEF Injector Supply Pipe Heater Resistance Is High

The electrical resistance in the heating element of the Diesel Exhaust Fluid (DEF) supply line (which prevents the DEF from freezing in cold temperatures) has exceeded the maximum allowable threshold. High resistance typically points to a failing heating element, a damaged wire, or a poor connection.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724
• 7600 Series Interim Tier 4 (2012-2015)

1. 1

   Access Diagnostic Mode: Use the tractor's display panel or a dedicated diagnostic tool to verify if the code is active or stored.

2. 2

   Visual Inspection: Inspect the wiring harness running from the ECU to the DEF injector supply pipe heater. Look for chafed wires, melted insulation, or physical damage.

3. 3

   Connector Check: Disconnect the DEF supply pipe heater connector. Check for corrosion, moisture, or bent pins, which can artificially increase circuit resistance.

4. 4

   Multimeter Resistance Test: Measure the resistance (Ohms) across the pins of the DEF supply pipe heater element itself. If the reading is out of specification (showing infinite resistance/open circuit or abnormally high Ohms), the heater has failed internally.

5. 5

   Voltage Check: Turn the key to the ON position and verify that the ECU is supplying the correct reference voltage to the heater circuit.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical shorts.

2. 2

   Clear the Area

   Locate the DEF injector supply pipe, which routes DEF from the pump/tank module to the DEF injector on the exhaust SCR system. Clean the area around the fittings to prevent dirt from entering the DEF system.

3. 3

   Remove the Faulty Pipe

   Disconnect the electrical connector for the pipe heater. Depress the quick-release tabs on the fluid fittings at both ends of the supply pipe and carefully remove the line. *Note: Have a rag ready, as some residual DEF may spill.*

4. 4

   Install the New Pipe

   Route the new DEF injector supply pipe in the exact same orientation. Push the fluid fittings onto their respective ports until they "click" and lock into place.

5. 5

   Reconnect Electricals

   Plug the heater electrical connector back into the main harness, ensuring the weather seal is intact.

6. 6

   Re-energize and Clear Codes

   Reconnect the battery. Turn the key on, use a diagnostic tool or the dash display to clear the 004346.03 fault code from the ECU, and run the tractor to ensure the code does not return and there are no DEF leaks.